This invention relates to a heavy duty blow molded wheel adaptable for many purposes but described in this application for particular use with a roll-out waste container of the type commonly used by waste haulers and municipalities for "street-side" waste collection.
One-piece molded plastic wheels are known in the prior art. However, prior art wheels are designed to resemble older-type pneumatic or semi-pneumatic wheels. Generally, this means that the side wall and tread portions of the plastic wheel are designed to resemble the rubber tire portion of a pneumatic or semi-pneumatic wheel, included a rounded tread area and a rounded, relatively thick width side wall.
There are, of course, reasons why a pneumatic tire has a rounded tread and side wall cross-section. Since the tire is filled with pressurized air, the tire will naturally want to assume a rounded cross-section since the air is pressing with equal force on all interior parts of the tire. Furthermore, since a pneumatic tire is designed to compress under weight and to absorb and cushion irregularities in the rolling surface, a relatively thick width side wall is required so that the tire will not be compressed to the point where the tread bottoms out on the wheel rim under heavy impact or weight loads. In other words, the side wall needs to be benefits offered by pneumatic and semi-pneumatic rubber tires.
These considerations to not apply in the use of plastic wheels. Plastic wheels are relatively stiff and brittle in comparison to rubber tires. Of course, plastic wheels are not pneumatic. They are generally used in situations where loads are not great, and on relatively even surfaces where it is not necessary to cushion impact on the wheel, for example on roll-out waste containers.
However, roll-out waste containers are becoming larger and are designed to carry much heavier loads. For these reasons, conventionally designed plastic wheels are now subject to crushing due to heavy loads placed on them. This crushing usually occurs in the side-wall area, which has a relatively thin cross-sectional dimension. Since the side wall area is generally perpendicular, or normal, to the direction of load application, the side walls are caused to bulge out under load. The relatively brittle plastic is not designed to flex to any substantial degree, and for this reason the side wall breaks down, damaging the wheel and eventually requiring replacement.
Of course, the cross-sectional thickness of the side wall can be made progressively greater to withstand heavier loads, or the volume occupied by the side walls and the tread could even be made nearly or completely solid. However, this complicates the molding process, uses more plastic material, and results in a heavier wheel.
It has been discovered that a wheel which will withstand heavy-duty loads without damage can be made using no more or even less material by substantially reducing the width of the side walls in proportion to the width of the wheel tread. The width of the side wall is therefore substantially smaller in relation to its own cross-sectional thickness, and the side wall is able to withstand much greater loads.